Riboflavin, also known as vitamin B2 is a physiologically active substance that is classified as a water-soluble type of vitamin. This riboflavin is said to aid in preventing and treating many eye diseases including cataracts, sometimes ameliorating symptoms such as inflammation, drying or itching of the eye, and eye strain. As for the physiological activities of riboflavin, it has been reported that riboflavin-containing compounds have an immunolo-augmenting action (Patent Document 1) and that riboflavin-containing compounds are useful as a toxin shock preventing or treating agent (Patent Document 2).
Further reports have been made on the analgesic action of riboflavin as one of its physiological activities. Examples include the following reports: that riboflavin ingested in high doses was effective for migraine prophylaxis (Non-patent Document 1); that riboflavin showed an analgesic action against inflammatory pain in a dose-dependent fashion when it was administered intraperitoneally at concentrations of 3 to 100 mg/kg but it was ineffective against pain in the nervous system (Non-patent Document 2); that when riboflavin was administered perorally at concentrations of 1 to 50 mg/kg, its analgesic effect in a formaldehyde test peaked at 25 mg and did not rise any further even when the dose was increased up to 75 mg (Non-patent Documents 2 and 3).
It has been known that B vitamins including vitamin B2 have anti-fatigue actions, namely, the fatigue relieving and preventing actions of B vitamins are known (Patent Document 3). In addition, supplements and drinks that contain vitamin B1, vitamin B2 and vitamin B6 are commercially available for ingestion by consumers who are fatigued or have rough skin.    [Patent Document 1] JP 5-201864 A    [Patent Document 2] JP 10-29941 A    [Patent Document 3] JP 2005-23008 A    [Non-patent Document 1] Schoenen J., NEUROLOGY, 50, 466-470, 1998    [Non-patent Document 2] European Journal of Pharmacology, 421, 157-164, 2001    [Non-patent, Document 3] European Journal of Pharmacology, 492, 35-40, 2004